1. Field of the Invention
This invention relates to a photographic material and a process for forming images, and more specifically, to a photographic material and a process for recording non-silver images at high sensitivity using a small amount of silver halide.
2. Description of the Prior Art
Conventional silver halide photographic methods and silver halide diffusion transfer methods have heretobefore been used widely as high-speed photographic processes. Silver halide photographic methods are described in detail, for example, in C. E. K. Mees and T. H. James, The Theory of the Photographic Process, MacMillan, New York, (1966), and silver halide diffusion transfer methods are described in A. Rott and E. Weyde, Photographic Silver Halide Diffusion Processes, The Focal Press, London and New York, (1972). A photographic material having a somewhat high sensitivity was developed and is comercially available under the trademark "DRY SILVER" (Minnesota Mining & Manufacturing Co.). This technique is described in detail in U.S. Pat. Nos. 3,152,903, 3,152,904, and 3,457,075.
These photographic processes have their own characteristics such as high speed, high quality, rapid processing, or dry processing, but they generally require large amounts of silver because silver compounds are used as the photosensitive substance and as the image-forming substance (or as an intermediate medium for color image formation in the case of silver halide color photographic processes). The recovery and re-use of silver are performed only in some of these processes because of the need for equipment, for example. This generally renders these photographic processes expensive. Furthermore, since concern exists as to the scarcity of silver resources, this is a disadvantage of photographic processes using silver.
Thus, development of photoraphic processes using low amounts of silver, or of non-silver photographic processes using no silver is necessary. A number of non-silver photographic processes have been reported (e.g., as described in J. Kosar, Light-sensitive Systems, John Wiley & Sons, New York, (1965)), but they generally have a much lower sensitivity than photographic processes using silver.
A physical developing method using a non-silver metallic ion is known as an example of a method for forming images by using a non-silver metal together with a small amount of a silver compound or non-silver compound as a photosensitive component or catalyst component. This method comprises exposing a sheet containing a small amount of a silver or non-silver compound as a photosensitive substance to form a development nucleus either directly, or indirectly by a subsequent treatment, or deactivating an active development nucleus initially present by exposure, and then dipping the sheet containing the development nucleus in a solution (physical development solution) composed of a non-silver metal ion (image-forming substance) and a reducing agent, etc. thereby selectively reducing the non-silver metal ion on the development nucleus and depositing the resulting metal atom on the development nucleus to form a non-silver metal image. The development nucleus is formed by various methods, for example, a method comprising exposing a photo semiconductor such as titanium dioxide and then resulting it with a silver ion or palladium ion to form a silver nucleus or palladium nucleus a method comprising exposing a diazonium compound to cause cis/trans isomerization, and reducing silver and a mercury ion with the isomerization product to form a silver amalgam nucleus, a method comprising exposing a photo-reducible dye and reducing silver ion, etc. with the resulting reducing agent to form a silver nucleus, etc., and a method comprising photo-decomposing a photosensitive noble metal compound such as a palladium compound to form a noble metal nucleus. On the other hand, copper, nickel, cobalt, and tin are known as examples of image-forming metals. The details of these physical development methods are described, for example, in U.S. Pat. Nos. 3,512,972, 3,893,856, 2,609,295, 2,733,144, 2,738,272, 2,750,292, 2,764,484, and 2,775,773, H. Jonker et al., Photographic Science and Engineering, Vol. 13, page 1 (1969), Vol. 13, page 33 (1969), Vol. 13, page 38 (1969), and Vol. 13, page 45 (1969), and H. Jonker et al., Journal of Photographic Science, Vol. 19, page 96 (1971). According to this photographic process, amplification is performed to some extent in the physical development step so that images can be recorded with a somewhat high sensitivity. However no method has ever been found in which developed silver directly formed from silver halide is used as a nucleus for the physical development of a non-silver metal. Accordingly, it is difficult to record images at high sensitivity comparable to that achieved with silver halide photography. The physical development method has other defects. For example, since a physical development solution containing both a reducible metallic ion as an image-forming substance and a reducing agent is generally unstable, the metallic ion tends to be reduced in the developer solution, and fog tends to occur. Moreover, the loss of the metallic ion is not small, and the used developer solution tends to cause pollution due to its heavy metal ion content.
Recently, photographic processes using photosensitive copper complexes were reported in U.S. Pat. Nos. 3,859,092, 3,860,500, 3,860,501 and 3,880,724. These processes involve exposing a sheet containing a certain monovalent or divalent copper ion complex, which is photosensitive to ultraviolet rays, to irradiation with ultraviolet rays, and then developing the exposed image by physical or chemical development to record a colored non-silver metal image. When images are to be obtained by physical development, these processes are not free from the various defects described above. But the characteristic of these processes is that images can be formed by chemical development (i.e., treatment with a reducing agent solution). In the case of chemical development, the element containing the copper complex is an "inner type" photographic material which both acts as a photosensitive component and an image forming component. However, since these processes are based on the utilization of the photosensitivity of the copper complex itself, image recording at the high speeds achieved in silver halide photographic materials is difficult. Furthermore, since this photographic material is not sensitive to visible light rays, it cannot be used for general photographic purposes.